There are some things even God cannot do. He cannot force anyone to freely accept Him. Forced freedom is a contradiction in terms. This is why Jesus said, Jerusalem, Jerusalem, you who kill the prophets and stone those sent to you, how often I have longed to gather your children together, as a hen gathers her chicks under her wings, but you were not willing. (Matthew 23:37) So the only way God could literally destroy all evil is to destroy all freedom.